The Relationship Between Tears of the Peroneus Brevis Tendon and the Distal Extent of its Muscle Belly: An MRI Study

Background: Anomalous distal insertion of the peroneus brevis muscle belly has been implicated as a possible etiology of tears of the peroneus brevis tendon. The purpose of this study was to assess whether patients with operatively confirmed tears of the peroneus brevis tendons have a more distally located musculotendinous junction. Methods: A retrospective review was done to identify all patients in whom direct inspection of the peroneal tendons was done between 1999 and 2004. The operative reports were evaluated, and all in whom a peroneal tendon tear was confirmed were included in the study group, Group I (29 patients). Group II represented an operative control group and consisted of all patients who had operative inspection of the peroneal tendons but did not have a tear (30 patients). Group III represented a radiographic control group and consisted of patients who had MRI of the ankle for reasons unrelated to lateral ankle symptoms (30 patients). For each patient, the vertical distance from the musculotendinous junction of the peroneus brevis tendon to the tip of the fibula was measured on sagittal MRI. The role of gender also was examined. The average distance between the musculotendinous junction of the peroneus brevis tendon to the distal fibula was calculated solely for men and women in all three groups. Statistical comparison of the groups was performed using the Mann-Whitney test. Interobserver reliability was determined by calculating Cronbach's Alpha coefficient. Results: The average distance from the musculotendinous junction to the tip of the fibula was 33.1 cm, 41.2 cm, and 46.3 cm in Groups I, II, and III, respectively. The average distance in Group I was statistically significantly lower than the average distance in both Groups II and III (p < 0.05). Interestingly, the difference in the distance between Groups II and III also was statistically significant (p < 0.05). The average distances in both men and women were statistically significantly different (p < 0.05) among the three groups. Conclusion: It has been hypothesized that tears of the peroneus brevis tendon result from distal insertion of the peroneus brevis muscle belly. This study provides radiographic support for this hypothesis.